Many communication protocols exist that provide bidirectional communication between two nodes (i.e. electronic devices) which, as part of the protocol, allow for discovery of nodes that are present on or connected to the communication medium. For example, protocols such as Bluetooth, WiFi and UPnP all allow a node to discover the identity and/or name of other active nodes (i.e. active in the sense that the nodes are broadcasting their name over the communication medium and/or are open to interrogation by and/or communication with, other nodes).
In general terms, communications in these protocols consist of two phases, and these phases are illustrated in FIG. 1. In a first phase 2, termed the ‘device discovery phase’, a node 4 wishing to initiate communications with another node 6, 8 queries the communication medium (i.e. over the air interface), which is represented by Query signals 10 in FIG. 1, to determine the nodes 6, 8 that are able to communicate with the initiating node 4.
Any node 6, 8 that is active (i.e. its transceiver circuitry is powered) and discoverable (i.e. open to establishing communications with another node) will reply to a received query signal 10 with its name (shown as “NameNode1 ” 12 and “NameNode2 ” 14 in FIG. 1) and numeric identifier.
Once the names and identifiers for nodes 6, 8 available for communication have been discovered, the initiating node 4 can establish a bidirectional communication channel 16 with the desired node (Node 1 in FIG. 1) in the second phase 18. The initiating node 4 and desired node 6 can then exchange data according to the communication protocol.
In these types of protocol, the first phase 2 is usually rigidly defined requiring a minimal amount of information to be exchanged between the nodes—typically only a text-based name for the node and a numerical identifier (such as a MAC address, which can be unique to the node). The rigid definition of this phase allows it to be very reliable and uniform (which allows every node implementing the protocol to understand and follow it. The second phase 18 often involves the freeform exchange of data (in some cases it is not limited by the length of data exchanged or its format). Because the second phase 18 is more loosely defined, communications between nodes are less reliable due to potential differences in the way in which the nodes individually implement the second phase 18 of the protocol.
For a range of types of electronic devices, it is necessary to provide a highly reliable communication channel to allow (sometimes only small amounts of) information to be conveyed to another device, while minimising the power consumed by such devices. Using a full two-phase communication protocol may introduce reliability problems due to the freeform nature of the second phase 18 of the protocol as described above, and may prolong the communication itself unnecessarily, which in turn might result in unnecessary power consumption.
Such devices include those used in a home healthcare and/or clinical healthcare settings. Many elderly people now carry or wear personal help buttons (PHBs) or personal emergency response systems (PERS) that they can activate if they need urgent assistance, such as when they fall. Automated fall detectors are available that monitor the movements of the user and automatically trigger an alarm if a fall is detected. Devices are also available that monitor the physiological characteristics of the user and to periodically or intermittently report the user's current status or an emergency condition.
These devices (i.e. PHBs, PERS, fall detectors and other monitoring devices) can initiate a phone call via a base unit located nearby to the user (i.e. typically in the user's home) to a dedicated call centre when they are activated, and the personnel in the call centre can talk to the user and arrange for assistance to be sent to the user in an emergency.
Thus, when an event is detected by the wearable device (for example the device detects a fall by the user, the user presses the help button or otherwise triggers the emergency response system), the device will need to communicate the occurrence of the event to the base unit through a wireless communication channel, so the base unit can initiate a call to a call centre or emergency services in order to get help to the user. In order to maximise the battery life of these devices (for example to allow the devices to used for weeks or months at a time without having to recharge or change the batteries, which is particularly desirable for elderly users), the wearable device does not actively communicate with the base unit until it becomes necessary (e.g. when the wearable device needs to convey the occurrence of an event or to inform the base unit of the current status of the wearable device). Thus, there may be no established communication channel between the wearable device and the base unit when an event occurs.
Therefore, there is a need for an improved method for reliably communicating information from a first node to a second node using minimal power in the first node.